Evolution of the Chicago Classification: Bridging Physiology and Mechanics

Swallowing difficulties are extremely common and result in substantial morbidity, reduction in the quality of life, and mortality related to malnutrition and complications from regurgitation and aspiration. Unfortunately, our understanding regarding the pathophysiology of dysphagia and GERD has been hampered by focusing predominantly on circular muscle activity and ignoring the essential biomechanical properties of the esophageal wall that promote normal emptying. Our initial work explored the relationship between intrabolus pressure (IBP) and esophagogastric junction (EGJ) compliance as a metric for outflow resistance. This work highlighted the direct relationship between IBP and EGJ opening and was the foundation for the development of the classification scheme utilized around the world to diagnose esophageal motor disorders: "the Chicago Classification" (CC). Despite this improved understanding focused on bolus transit dynamics, there are still significant gaps in our scientific understanding centered on the lack of a true correlate for symptoms, reliable predictive models and effective treatments for Functional dysphagia, IEM and EGJOO. Given these limitations, we have developed novel approaches that combine assessments of primary and secondary peristalsis (a NeuroMyogenic Model of esophageal function). These will leverage our recent findings supporting the importance of the esophageal response to distension in bolus clearance, noting that this response of the esophageal wall to bolus retention or reflux is one of the most essential functions of the esophagus in preventing complications of aspiration, or reflux injury. We will also include an assessment of esophageal geometry and wall biomechanics (elasticity/dilatation) as these carry essential interactions with esophageal function that are overlooked in the current diagnostic paradigms.

In order to test our hypothesis that wall mechanics are a major determinant of esophageal diseases, we had to develop new approaches and new technology to directly measure mechanical wall state, descending inhibition and LES opening. Using impedance techniques combined with manometry, we are now capable of assessing IBP and diameter changes across a space-time continuum (4D HRM). We also developed physics-based hybrid diagnostics that include a FLIP technique to assess esophageal work and power during volumetric distention (FLIP-MECH) and a fluoroscopy approach that simultaneously assesses esophageal diameter-pressure relationships (Fluoro-MECH). We also developed a new approach, Interactive FLIP Panometry, which facilitates an assessment of descending inhibition and the mechanism behind impaired LES opening. These tools will allow us to expand our models to combine an assessment of neuromyogenic function simultaneously with geometry. Our overarching goal will be to study well-defined patient populations (Functional Dysphagia, IEM/GERD, EGJOO and Achalasia) before and after targeted interventions to test the NeuroMyogenic and MechanoGeometric Model. This work will build upon the previous success of the CC and help advance the evolution of the CC by defining new, relevant biomechanical physiomarkers of disease activity that can identify new targets for therapeutic intervention and facilitate prediction of clinical outcomes.